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COMPUTING SCIENCE

Connecting the Dots

Can the tools of graph theory and social-network studies unravel the next big plot?

Brian Hayes

In the five years since that wrenching Tuesday morning when hijacked aircraft sliced into the World Trade Center and the Pentagon, Americans have been living with a new undercurrent of worry and mistrust. Naturally, there's fear of further attacks. But there's also concern that measures taken to forestall such attacks could erode traditional rights and liberties. In recent months, controversy has erupted over reports that government agencies are monitoring Internet and telephone communications as well as financial transactions. Some of the surveillance programs are said to be sifting through gigantic data sets, scanning for patterns that might reveal criminal intent or activity.

A map of a social network...Click to Enlarge Image

The debate over these programs has focused mainly on legal and political questions. Are constitutional and statutory safeguards being respected? What about laws that bar intelligence agencies from spying on American citizens? Do the programs strike an appropriate balance between the right to privacy and the need for security? These are important issues, but I shall leave them to others. Here I want to ask a different kind of question: What can one expect to learn through such wholesale screening and data-mining operations? Do the communications patterns of terrorists have a signature so distinctive that computer algorithms can detect signs of a conspiracy amid trillions of other telephone calls or e-mail messages?

In addressing these questions I face an obvious impediment: Very little reliable information on the nature and scope of the surveillance programs has been made public. However, mathematicians and computer scientists have tackled problems very similar to those confronting an intelligence analyst trying to make sense of surveillance data. And social scientists have long taken an interest in the networks that bind people together—including networks of criminals and terrorists. Perhaps by combining insights from these fields we can make some plausible guesses.





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